1. Field of the Invention
The present invention relates to a semiconductor memory device and method of controlling the semiconductor memory device.
2. Description of the Related Art
In recent years, as the next generation semiconductor memory device, the following devices have been developed; a ferroelectric random access memory (FeRAM), a magnetic random access memory (MRAM), a phase change random access memory (PRAM), a resistive random access memory (RRAM), an ovonic unified memory (OUM) and the like. The RRAM and OUM are semiconductor memory devices using diode characteristics. As a type of diode used in the RRAM or OUM, a pn diode formed on a semiconductor substrate such as a silicon substrate is used (refer to Japanese Patent Translation Publication No. 2006-505939 (pp. 26, FIG. 1) and International Publication WO2003/028124).
In the diode described in Japanese Patent Translation Publication 2006-505939, the operation of the diode requires an application of a voltage equivalent to the forward voltage (Vf) of the pn diode, for example, a voltage not less than 0.7 V. For this reason, there is a problem that it is difficult to perform an operation at a low voltage not greater than Vf in the semiconductor memory device using the diode characteristics. Moreover, a silicon pn diode requires a heat treatment at a temperature substantially not less than 750° C. in order to activate the P layer or the N layer. For this reason, there is another problem that it is difficult to manufacture, at a relatively low temperature, a semiconductor memory device using the diode characteristics.